Re: [RFC] distinguish foreground and background IOs in block throttle

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> Il giorno 25 dic 2017, alle ore 03:44, xuejiufei <xuejiufei@xxxxxxxxx> ha scritto:
> 
> Hi all,
> 
> Cgroup writeback is supported since v4.2. I found there exists a
> problem in the following case.
> 
> A cgroup may send both buffer and direct/sync IOs. The foreground
> thread will be stalled when periodic writeback IOs is flushed because
> the service queue already has a plenty of writeback IOs, then
> foreground IOs should be enqueued with its FIFO policy.
> 
> I wonder if we can distinguish foreground and background IOs in block
> throttle to fix the above problem.
> 
> Any suggestion are always appreciated.
> 

Hi,
to address similar issues, I have just sent a patch [1] for the BFQ
I/O scheduler.  If you want to give it a try, it might solve, or at
least mitigate, your problem (the patch does not involve groups,
though, at least for the moment).

There are still pending patches related to the low_latency mode of
BFQ, so I suggest you to try with low_latency disabled, i.e., as root:
echo bfq > /sys/block/<your-device>/queue/scheduler
echo 0 > /sys/block/<your-device>/queue/iosched/low_latency 

For your possible convenience, I have attached the patch, gzipped, to
this email too.

Thanks,
Paolo

[1] https://www.spinics.net/lists/kernel/msg2684463.html

Attachment: 0001-block-bfq-limit-tags-for-writes-and-async-I-O.patch.gz
Description: GNU Zip compressed data


> 
> Thanks,
> Jiufei


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